Sound directing apparatus



March 15, 1960 PAUL-FRIEDRICH WARNING 2,

SOUND DIRECTING APPARATUS Filed April 50, 1957 FIG.

INVENTOR. PAUL- F RIEDRICH WARNING- SQUN D DIRECTIN G APPARATUS:

Paul-Friedrich Warning, Wennehostel, Post Bissendorf,

Hannover, Germany, assignor to Fir-ma Sennlieiser Electronic Dr. Ing. Fritz Sennheiser, 'Wennehostel, Bissendorf, Hannover, Germany Application April 30, 1957, Serial No. 656,142 llClaiins. (Cl. 181-.5)

The present invention relates to an electroacoustic transducer. arrangement. More particularly, the present invention. relates to a sound directing member for use with el'ectroacoustic transducer apparatus.

In order to make unidirectional electroacoustic transducers such as microphones and loudspeakers, it is desirable and advantageous to have sound directing elements wherein the sound waves applied to the sound directing elements in a desired direction pass through to the electroacoustic transducer while the sound waves applied inv all other directions are attenuated. Some arrangements have been developed wherein elongated tubular members are used having sound wave permeable portions. 'Ilte permeability of these portions to sound waves'applied thereto vary in a direction parallel to the axis of the. tubular member. Accordingly, sound waves which are applied to the tubular member in a direction trans,- verse to the axis thereof pass through the sound permeable portions and are attenuated by the interference patterns set up between the sound waves.

On, the other hand, sound waves applied to the elongatedmember in a direction parallel to the axis thereof pass through the tubular member with substantially no attenuation. Such a tubular member accordingly" has a lobe-shaped direction characteristic with the size of the lobe and the directional sensitivity thereof increasing with nited. States Patent 0 present invention, however, a plurality of spaced plate" members are provided to divide the space adjacent to;

and outside of, a continuous opening of the tubular memincreasingfrequency of the sound waveapplied'thereto.

it is therefore very difilcult toattempt to use such a sound. directing tubular member for high frequencies since the higher the frequency, the smaller will be the'area covered by the tubular member. Similarly, the frequency dependent sound directing characteristic of such atubular member is such that the amplitude of the'sound waves applied transverse to the axis of the tube decreases even a greater amount with increasing frequency than sound waves applied parallel to the axis thereof.

If a microphone utilizing such sound directing apparatus is used in halls or enclosures wherein the sound reverberates and is reflected from the walls thereof the reflected sound is proportionally larger than the original sound. Accordingly, the reproduced sound has a very hollow or muffled tonal quality. Since the frequency characteristic of the microphone system cannot be-arbitrarily' varied to match the sound directing apparatus, it is necessary to increase the amplitude of the sound'waves occurring at higher frequency in some other manner.

The sound permeable portion of the tubular sound directingv apparatus for the microphone system can be formed with a plurality of holes through the inner and outer faces of the tubular member so that eachhole or opening is equivalent to a small exponential horn. These small exponential horns produce a pressure transforma I tion to improve the response of the microphone with re-' spect to high frequency.

In the event that the sound permeable portion of the tubular member is formed as a single continuous opening through the inner and outer faces of the tubular meniber in a direction parallel to the axis thereof, such small her into a plurality of horn elements for providing an improved frequency response of the sound directingtubw lar member.

It is accordingly an object of the present invention to.

provide a new and improved sound directing apparatus for use with electroacoustic transducer elements.

A second object of the present invention is'toprovide sound directing member for electroacoustic transducers,. which sound directing member has improved high frequency characteristics.

Another object of the present invention is to provide a sound directing member in the form of an elongated tubular member having a sound permeable portion in'the form of a continuous opening through the inner and outer faces of the tubular member and having improved high frequency characteristics.

With the above objects in view, the present invention mainly consists of an electroacoustic transducer arrange ment including an elongated tubular member for directing sound waves applied thereto in a desired direction, the tubular member having at least a sound wave perme' able portion, the sound Wave permeability of which varies in a direction substantially parallel to the axis of the elongated member, and a plurality of spaced plate members arranged along the tubular member adjacent to the sound wave permeable portion thereof and outside the same, the "plate members thereby being capable of im proving the high frequency characteristics andofcau'sing attenuation of sound waves directed in a direction different from the desired direction while sound waves applied in' the desired direction pass through the tubular member substantially without attenuation thereof.

In a preferred embodiment of the present invention the plate members are planar, parallel to each other, equally spaced in longitudinal direction from: each: other and arranged substantially transverse to" the axis of the tubular member.

In another embodiment of the presentinvention the tubular memberit'self is made from soundpermeable material and'the plate members may be'annuleir mem' bers' arranged about the tubular member substantially transverse to the axis thereof.-

The novel features which are considered as characteristic for the invention are set forth in particular inthe appended claims. The invention: itself, however, bet. as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection. with the accompanying drawings, in which:

Fig. 1 is a side elevationalviewof a sound: directing member constructed in accordance withthepresent in vention;

Fig. 2 is a crosssectional end viewof the embodiment shown" in Fig. l, the section being. taken along line II-II in Fig. l;

Figs. 3, 4, 5 and 6 are respective similar. cross-sectional end views of different embodiments of the presentinvem tion; and

Fig. 7 is a graphical representation of the frequency response of the sound directing apparatus incorporating the principles of the present invention compared to con; ventional arrangements.

Referring to the drawings, and more particularly to Figs. 1 and 2 it can be seen that the sound directing member includes an elongated tubular member 1 haviirgan opening slit 4 passing through the inner and outer Patented Main 15,1960

6 faces of the tubular member 1 and extending in a direction substantially parallel to the axis of the tubular member.

Arranged about the outer face of the tubular member 1 is a sound permeable member 2 adjacent to the opening 4 and extending lengthwise along the tube to substantially cover the opening 4. Mounted on the sound permeable member 2 is a plurality of spaced plate members 3 made of solid material. The distances between each pair of adjacent plate members 3 are respectively equal. This distance is also preferably less than A of the wave length of the highest frequency sound wave to be transmitted.

The sound permeable member 2 can have a sound permeability characteristic which varies in a direction parallel to the axis of the tubular member 1. This is advantageous since a microphone or loudspeaker element which can be arranged adjacent one end of the tubular member 1 will receive sound waves which are attenuated substantially the same amount regardless of the length of the path travelled by the sound waves.

Each pair of adjacent plate members 3 forms a distorted horn element when taken in conjunction with the portion of the opening 4 arranged therebetween. That is, the opening 4 arranged between a pair of plate members 3 forms the neck portion of the horn through which the sound passes while the plate members 3 form the remainder of the horn for the sound waves.

In addition to the spacing between the plate members 3, the upper limiting frequency of the plate member arrangement is also determined by the distance of the outer periphery 3 of each plate member 3 from the opening 4. The cross section of such a horn arrangement increases an amount which is proportional to the distance from the throat 4 of the horn.

In operation, sound waves applied to the sound directing'tubular member shown in Figs. 1 and 2 in a desired direction will pass through the tube 1 substantially with no attentuation thereof. The sound waves applied to the sound directing tubular member in any other direction will be attenuated by the interference patterns set up between such sound waves in the tubular member 1.

In the embodiments described in Figs. 1 and 2, the proportional change of cross section with respect to distance of the cross section from the throat of the horn matches the horn to the applied sound waves with a certain acoustic impedance. This acoustic impedance can be improved somewhat if the cross section of the horn increases more quickly with respect to the distance between the cross section and the throat of the horn. Such an arrangement is shown in Fig. 3.

In Fig. 3, the tube 1 having the opening slit 4 therein is arranged in the same manner as the embodiment shown in Fig. 1 or 2. In addition, the sound permeable member 2 is arranged on the outer face of the tubular memher 1 adjacent opening 4. In this embodiment a plurality of spaced discs 5 are arranged wherein the outer periphery of each disc is no longer substantially circular with its center substantially coinciding with said opening 4 but is eccentric thereto so that the cross section of each horn formed between adjacent plate members 5 increases with distance from the throat of the horn in a manner much faster than a proportional manner.

Arranged adjacent the periphery of each disc 5 opposite the opening 4 and passing through each disc is a rod member 6 which provides support for the discs 5 so that they maintain their proper spacing positions. In addition, the position of the rod 6 improves the acoustic impedance of the plurality of horns, each formed by two adjacent plate members 5 and the adjacent surfaces of memher 2 and rod 6, with the respective portion of the opening 4 therebetween acting as neck thereof. In this manner, the embodiment of Fig. 3 provides a more efficient matching between the sound waves in the region surrounding the sound directing apparatus and the tubular member 1 through which the desired sound waves pass.

Referring now to Fig. 4, an arrangement is shown wherein a tubular member 7 is provided, substantially all of which is made from a sound permeable material. In this embodiment, a plurality of annular plate members 8 are arranged in spaced parallel position along the axis of the tube 7. These annular members 8 are preferably equally spaced from each other.

In this arrangement, the matching between the sound waves and the tube 7 is good for a very small zone. In the arrangement of Fig. 3 the amplitude of the sound waves passing through the tube 1 was increased and a better matching impedance was provided by arranging the cross section of the plurality of horns to increase in a manner substantially more quickly than a proportional manner with respect to the throat of the horn. Such an improvement is not easy to obtain with the arrangement of Fig. 4.

However, the zone in which the embodiment of Fig. 4 is eifective can be improved somewhat by increasing the distance between the outer periphery of each of the members 8 and the tube 7.

Referring to Fig. 5, annular members 9 are shown wherein the outer periphery of a portion of the plate members 9 is substantially farther from the tube 7 than the remainder of the members 9. In this arrangement the throat of each horn is arranged eccentrically with respect to the outer periphery of the size of the horn while in the arrangement of Fig. 4, the threat is concentrically arranged. The advantageous impedance arrangement of Fig. 5 can also be produced by providing a narrower throat portion for the sound waves.

Referring now to Fig. 6, an embodiment is illustrated having a tubular member 1 and a sound permeable member 2 as shown in the embodiments of Figs. 2 and 3. However, in this arrangement plate members 11 are arranged so that the path followed by the sound waves passing through the horn formed between adjacent plate members 11 is longer than in the embodiments shown in Figs. 2 and 3. This is equivalent to the improvement provided by the embodiment of Fig. 5 with respect to the embodiment illustrated in Fig. 4.

The improved response of the apparatus incorporating the principles of the present invention can be seen from the graphical representation of Fig. 7 wherein the frequency ;f of the sound waves passing through the sound directing apparatus is plotted on the X axis while the amplitude of the sound waves is plotted on the Y axis. The curve 12 shows the frequency response of conventional tubular arrangements not provided with the improved impedance matching elements formed by the plate members arranged about the outer face of the tubular member. The curve 13 corresponds to the frequency response obtained with the arrangement shown in Fig. 2

while the curve 14 corresponds to the arrangement shown in Fig. 3.

Since the positioning and mounting of a large plurality of plate members to provide the proper acoustic impedance is fairly complicated, it is advantageous to form the plate members together with the rod member 6 out of a material which can be produced by injection molding. In

this manner it is not necessary to mold the entire length changes may be made without departing in any way from the spirit of the present invention.

elongated tubular member for directing sound waves applied thereto in a desired direction, said tubular member having at least a longitudinally extending sound wave permeable portion, the sound wave permeability of which varies in a direction substantially parallel to the axis of said elongated member; and a plurality of longitudinally spaced transverse plate members arranged along and outside said tubular member adjacent to said sound wave permeable portion thereof.

2. In an electroacoustic transducer, in combination, an

elongated tubular member for directing sound waves ap-' plied thereto in a desired direction, said tubular member having at least a longitudinally extending sound wave permeable portion, the sound wave permeability of which varies in a direction substantially parallel to the axis of said elongated member; and a plurality of equally spaced parallel planar plate members arranged in transverse position along said tubular member and outside the same and adjacent to said sound wave permeable portion thereof.

3. In an electroacoustic transducer, in combination, an elongated tubular member for directing sound waves applied thereto in a desired direction, said tubular member\being formed with an opening passing through the inner and outer face thereof and extending in a direction substantially parallel to the axis thereof; a sound permeable member mounted on one of the faces of said tubular member overlapping said opening, said sound permeable member having a sound permeability which varies in a direction substantially parallel to the axis of said elongated tubular member; and a plurality of longitudinally spaced plate members arranged in transverse position along said tubular member and outside the same and adjacent said sound permeable member.

4. In an electroacoustic transducer, in combination, an elongated tubular member for directing sound waves applied thereto in a desired direction, said tubular member being formed with an opening passing through the inner and outer face thereof and extending in a direction substantially parallel to the axis thereof; a sound permeable member mounted on the outer surface of said tubnlar member overlapping said opening, said sound permeable member having a sound permeability which varies in a direction substantially parallel to the axis of said elongated tubular member; and a plurality of longitudinally spaced plate members arranged in transverse position along said tubular member and outside the same and adjacent said sound permeable member.

5. In an electroacoustic transducer, in combination, an elongated tubular member for directing sound waves applied thereto in a desired direction, said tubular member having at least a longitudinally extending sound wave permeable portion, the sound wave permeability of which varies in a direction substantially parallel to the axis of said elongated member; a plurality of longitudinally spaced plate members arranged in transverse position adjacent to said sound wave permeable portion thereof, a rod member extending radially spaced from, and parallel with, said sound wave permeable portion, and connecting the individual plate members with one another.

6. In an electroacoustic transducer, in combination, an elongated tubular member for directing sound waves applied thereto in a desired direction, said tubular member being formed from a sound permeable material hav ing a sound permeability which varies in a direction substantially parallel to the axis of said tubular member; and a plurality of longitudinally spaced plate members arranged in transverse position along said tubular member and outside the same.

7. In an electroacoustic transducer, in combination, an elongated tubular member for directing sound waves applied thereto in a desired direction, said tubular member being formed from a sound permeable material having a sound permeability which varies in a direction substantially parallel to the axis of said tubular member; and a plurality of longitudinally spaced annular members arranged in transverse position along said tubular mem her and outside the same. i

8. In an electroacoustic transducer, in combination,

.an elongated tubular member for directing sound waves applied thereto in a desired direction, said tubular member having at least a longitudinally extending sound wave permeable portion, the sound wave permeability of which varies in a direction substantially parallel to the axis of said elongated member; and a plurality of longitudinally spaced plate members arranged in transverse position along said tubular member and outside the same and adjacent to said sound wave permeable portion there of in such manner that the sound wave permeable por tion between two adjacent plate members is centrally positioned with respect to the outer edge of said plate members.

9. In an electroacoustic transducer, in combination,

' an elongated tubular member for directing sound waves along said tubular member and outside the same and applied thereto in a desired direction, said tubular member having at least a longitudinally extending sound wave permeable portion, the sound wave permeability of which varies in a direction substantially parallel to the axis of said elongated member; and a plurality of longitudinally spaced plate members arranged in transverse position along said tubular member and outside the same and adjacent to said sound wave permeable portion thereof in such manner that the sound wave permeable portion between two adjacent plate members is eccentrically positioned with respect to theouter edge of said plate members.

10. An electroacoustic transducer as set forth in claim 3, including a rod member extending radially spaced from, and parallel with, said sound wave permeable portion, and connecting the individual plate members with one another.

11. An electroacoustic transducer as set forth in claim 7, said annular members being positioned eccentrically to said tubular member.

References Cited in the file of this patent UNITED STATES PATENTS 2,210,415 Kellogg Aug. 6, 1940 2,228,886 Olson Jan. 14, 1941 2,406,391 Mason Aug. 27, 1946 2,739,659 Daniels Mar. 27, 1956 2,856,022 Kurtze et al. Oct. 14, 1958 

